A fiber-optic gyroscope (FOG) measures a rate of rotation. In an example, the FOG does this by operating in the following manner: a beam of light in a FOG is split into two beams, the two beams travel around a sensing coil, exit the sensing coil and then measured in a detector. The detector measures the phase difference between the two counter propagating beams of light. The phase shift experienced by the two beams of light is proportional to the rate of rotation of the FOG due to the Sagnac effect. If any of the FOG's components deteriorate over time, the FOG can become less accurate in measuring the light's phase shift.